Think of how strong a kangaroo's thighs are
http://fanamorphs.cyoc.net/images/co...roo%20copy.jpg

Now, think of how much damage a kangaroo's foot could do!
http://www.ozanimals.com/image/album...0402290035.jpg

Now, imagine the damage they could do to a pair of kangaroo balls, which are COMPLETELY weak, like any testicle. (not to mention completely open for attack!)
http://www.istockphoto.com/file_thum..._testicles.jpg